The Earth's climate has gone through many cycles that have caused significant fluctuations in the temperature of the Earth's surface. In the context of geological time, current global temperatures are in the middle range of those experienced by the Earth (ABS 2001). When viewed over a shorter period, however, a different picture can be seen (graph 14.29).

Australia's annual mean temperatures have increased since 1910, although the amount of increase has varied from place to place. In general, minimum temperatures have increased the most, particularily in the eastern half of Australia where they have increased by approximately one degree celsius (BoM 2000).

There is widespread national and international concern that it is the activities of people which have caused temperatures to increase worldwide (Watson 1999). Carbon dioxide and other 'greenhouse gases' are released into the atmosphere from the use of fossil fuels, and stored carbon has also been released through the clearing of vegetation. It is thought that increasing the concentration of greenhouse gases in the atmosphere increases its ability to absorb heat energy (UNEP & UNFCCC 1999). This has been termed the 'greenhouse effect' or 'enhanced greenhouse effect'. Projections indicate that annual average temperatures in Australia could be 0.4 to 2.0 degrees higher by 2030 and 1.0 to 6.0 degrees higher by 2070 (CSIRO 2001a).

The United Nations Framework Convention on Climate Change (The Framework Convention) established the first international treaty dealing with climate change and laid the basis for global action to "protect the climate system for present and future generations" (UNEP & UNFCCC 1999). Governments recognised the need for legally binding commitments to greenhouse gas emission limitations and reductions which were subsequently reflected in policy terms in the Kyoto Protocol. Australia negotiated to restrict its emissions increases to 8% above 1990 levels in the budget period 2008 to 2012. At the recent sixth Conference of Parties in Bonn, Germany, the international community (excluding the United States) agreed to reduce global greenhouse gas emissions by an average of around 2% by 2008-2012 (Pannell 2001).

According to the National Greenhouse Gas Inventory (NGGI), Australia's total emissions of greenhouse gases increased by 67.9 megatonnes of carbon dioxide equivalents (17.4%) between 1990 and 1999 (graph 14.30 and table 14.31). The rate of growth reached peaks of 3.6% in 1995 (mainly due to increases in emissions from the Manufacturing, Electricity generation and Transport sectors) and of 4.5% in 1998(largely due to an increase in Electricity generation emissions) (AGO 2001a).

While total carbon dioxide equivalent emissions increased by 17.4% between 1990 and 1999, the emissions of individual greenhouse gases that make up this total varied significantly. Emissions of carbon dioxide (CO2) increased by 25.5%, methane (CH4) emissions by 1.0% and those of nitrous oxide (N20) by 30.8% (table 14.31). Perfluorocarbons (PFC) and sulfur hexafluoride (SF6) were the only greenhouse gases to record a decrease in emissions over the period (79.2% lower in 1999 than in 1990). As a result of these changes, carbon dioxide increased its share of total emissions from about 64% to 68%.

14.31 GREENHOUSE GAS EMISSIONS, By Gas - 1990 and 1999

Greenhouse gases

1990Mt CO2-e

1999Mt CO2-e

ChangeMt

% Change in emissions

CO2

249.8

313.5

63.7

25.5

CH4

113.3

114.4

1.1

1.0

N2O

22.4

29.3

6.9

30.8

PFCs and SF6

4.8

1.0

-3.8

-79.2

Total CO2-e

390.3

458.2

67.9

17.4

Source: AGO 2001a.

The Australian economy is highly dependent on energy consumption. The combustion of fossil fuels is the major contributor to Australia's greenhouse gas emissions (around 73% of net emissions from stationary and transport energy combustion in 1999)(AGO 2001a). Fossil fuels provide around 90% of Australia's energy needs, a higher proportion than for most other countries or regions. The Stationary Energy sector (emissions from fuel combustion in energy industries such as the Electricity industry) is the biggest contributor of greenhouse gases (graph 14.32), accounting for 56.7% of net emissions in 1999, with electricity generation accounting for the majority of this sector's contributions (259.8 Megatonnes of CO2 equivalents). Energy use and resulting greenhouse gas emissions from the Stationary Energy and Transport sectors are described in further detail see Energy.

The Industrial Processes sector (emissions resulting from production processes) recorded a decrease in emissions in this period, from 12 Mt of CO2-e in 1990 to 9.7 in 1999 (almost entirely a result of reduction in PFC emissions from aluminium production).

Vegetation plays an important role in reducing the level of greenhouse gases in the atmosphere, as trees and other plants absorb CO2 from the air and store it as carbon. Under ideal conditions, 1 million hectares of new forest could absorb about 25 megatonnes of CO2 a year, which would lower Australia's present CO2 production by about 9% (CSIRO 2001b). The Forestry sector (including commercial forestry) is an emitter (source) and an absorber (sink) for CO2. Emissions from the Forestry sector are affected by both timber harvest and forest regrowth rates. Regrowth exceeded harvesting in each year of the period, but by a declining margin, so the net carbon uptake in 1999 was calculated as lower than in 1990. In 1999, carbon removals through the growth of forests were 75.8 Mt and forest harvesting gave rise to 52.8 Mt of emissions. This resulted in an uptake of greenhouse gases by the Forestry sector of 23.1 Mt, equivalent to 5.0% of total greenhouse gas emissions for 1999.

Current best estimates of land clearing model the emissions from burning cleared vegetation, decay of slash and below ground decay of roots, and loss of soil carbon. These estimates are highly uncertain and likely to change in the future.

Although our emissions are increasing, greenhouse gas emissions per dollar of GDP were 13.0% lower in 1999 than in 1990 (graph 14.33). This is because emissions grew at an average rate of 1.8% while economic activity grew at a significantly greater rate of 3.4% (AGO 2001a). Thus the emissions intensity of the economy declined over the period. Structural changes in the economy towards service industries have been important in the decreasing trend of greenhouse gas intensities.